When transmitting service data, a communication system encodes the service data to be transmitted through an encoding scheme adapted for a payload bandwidth.
Currently, a 64B/66B encoding scheme (converting a 64B encoding scheme into a 66B encoding scheme) for obtaining 66B coding blocks containing 64B or a 64B/65B encoding scheme (converting the 64B encoding scheme into a 65B encoding scheme) for obtaining 65B coding blocks containing 64B is commonly used in the 10 Gigabit Ethernet (10 GE) standard. FIG. 1 shows a structure of a 66B coding block. It can be seen that, the 66B coding block contains two types of payload blocks, which are identified by a Syn field occupying two bits, with Syn=01 representing a data block containing data only, and Syn=10 representing a control block containing control characters. There are 15 different types of control blocks containing control characters, which are identified by a Block Type Field occupying the first eight bits after the Syn.
The control character includes C code, O code, /S/ code, and /T/ code. The C code occupies seven bits, the O code occupies four bits, and the /S/ code and the /T/ code are removed according to the encoding rule during encoding.
A 65B coding block has a structure similar to that of the 66B coding block, except that the Syn field of the 65B coding block occupies only one bit.
With the increasing bandwidth requirements caused by the increase in people's demand for voice, data, multimedia, and other services, the OTN has gradually become a core platform for bearer services of various operators. Transmission of service data on the OTN using the 10 GE or 40 Gigabit Ethernet (40 GE) standard is currently considered a hot topic.
FIG. 2 shows a structure of an OTN frame. It can be seen that, the OTN frame includes an optical channel payload unit-k (OPUk) payload, an optical channel transport unit-k (OTUk) forward error correction (FEC), and the following overhead (OH) portion caused by transmitting the payload:
OPUk OH; optical channel data unit-k (ODUk) OH; and OTUk OH.
OPU types and capacity corresponding to the OPUk are as shown in Table 1.
TABLE 1OPU Payload bitOPU typeOPU Payload nominal bit raterate toleranceOPU12 488 320 kbit/s±20 ppmOPU2238/237 × 9 953 280 kbit/sOPU3238/236 × 39 813 120 kbit/sOPU1-XvX * 2 488 320 kbit/s±20 ppmOPU2-XvX * 238/237 * 9 953 280 kbit/sOPU3-XvX * 238/236 * 39 813 120 kbit/sNOTE -The nominal OPUk Payload rates are approximately: 2 488 320.000 kbit/s (OPU1 Payload), 9 995 276.962 kbit/s (OPU2 Payload) and 40 150 519.322 kbit/s (OPU3 Payload). The nominal OPUk-Xv Payload rates are approximately: X*2 488 320.000 kbit/s (OPU1-Xv Payload), X*9 995 276.962 kbit/s (OPU2-Xv Payload) and X*40 150 519.322 kbit/s (OPU3-Xv Payload).
It can be seen that, the payload bandwidth of the OPU2 is 9.995276962 GBits/s, and the payload bandwidth of the OPU3 is 40.150519322 GBits/s.
In order to transmit 10 GE MAC frames (containing data and control codes), a payload bandwidth of at least 10 GBits/s is required. However, since the payload bandwidth of the OPU2 of the OTN is 9.995276962 GBits/s, which is smaller than 10 GBits/s, the payload bandwidth required for transmitting 10 GE MAC frames in the OTN cannot be satisfied. Therefore, some companies proposed to extend the payload bandwidth of the OPU by using a portion of unused OPU and ODU overheads. FIG. 3 is a schematic view of an OH structure of the OTN frame. Referring to FIGS. 2 and 3, the OH suitable for extending the payload bandwidth of the OPU2 is analyzed in the following.
It can be seen from FIG. 3 that, nine Reserve (RES) bytes, namely, the first three RES bytes in the second row and six RES bytes in the fourth row in FIG. 3, may be used for bearing the load. Comparing FIG. 2 with FIG. 3, it can be seen that a portion in FIG. 3 corresponding to the OPUk OH in FIG. 2 includes a client specific portion and a payload structure identifier (PSI), and occupies eight bytes, in which the PSI occupies one byte and cannot be used for bearing the load, and the other seven bytes may be used for bearing the load. In this way, the 16 bytes may be used for bearing the load, thereby extending the payload bandwidth of the OPU2.
After the payload bandwidth of the OPU2 is extended, the payload bandwidth of the OPU2 may be increased to (3808*4+16)/(3808*4)*9.995276962 GBits/s=10.005776202 GBits/s. The value is slightly higher than the rate of 10 GBits/s. However, if the 10 GE uses the 64B/66B encoding scheme, a linear rate of (66/64)*10 GBits/s=10.3125 GBits/s is required, which is still higher than the increased payload bandwidth of the OPU2. Therefore, the payload bandwidth required for transmitting MAC frames of the 10 GE standard in the OTN cannot be satisfied if the 64B/66B encoding scheme is directly used.
In addition, in order to transmit 40 GE MAC frames, a payload bandwidth of at least 40 GBits/s is required. However, since the payload bandwidth of the OPU3 of the OTN is 40.150519322 GBits/s, which is higher than 40 GBits/s, the transmission of 40 GE MAC frames in the OTN may be achieved. However, if the 64B/65B encoding scheme is directly used for encoding 40 GE signals, a linear rate of 65/64*40 GBits/s=40.625 GBits/s is required. If the 64B/66B encoding scheme is used, a linear rate of 66/64*40 GBits/s=41.25 GBits/s is required. The two linear rates are both higher than the payload bandwidth of the OPU3 of the OTN. Therefore, the payload bandwidth required for transmitting MAC frames of the 40 GE standard in the OTN cannot be satisfied if the 64B/66B encoding scheme or the 64B/65B encoding scheme (with the Syn field being changed to one bit) is directly used.